Electrodeposition of copper



Patented July 12, 1949 ELECTRODEPOSITION OF COPPER Abraham M. Max,Indianapolis, Ind., assignor to Radio Corporation of America, acorporation of Delaware No Drawing. Application August 28, 1945,

Serial No. 613,215 r 2 Claims. (01. 204-52) This invention relates toelectroforming copper deposits, and more particularly to a copper plating solution from which fine-grain deposits of copper may be plated.

One of the aims of electroforming deposits of various metals is toobtain metal matrices the surfaces of which duplicate the surfaces onwhich electroforming takes place. The surface of an electroformed matrixis the negative of the original surface, the impressions or depressionsin the original surface becoming elevations in the electroformedsurface.

Acid copper plating solutions have been used heretofore forelectroforming copper deposits. Such solutions have the advantages,among others, that (1) they have comparatively wide limits of operation,(2) they can be easily controlled, (3) they provide smooth, heavydeposits of copper, and (4) they have the ability to cover a thin,conductive film on a non-conductive material. Hence, acid copper platingsolutions are preferred to other types. However, copper depositsobtained from an acid copper plating solution are very soft and have atendency to tree. Consequently, addition agents are employed to produceharder and smoother deposits.

Electroformed copper deposits from an acid copper plating solutionconsists of columnar crystals perpendicular to the starting surface, orsurface on which the copper is being plated, the crystals becominglarger, by lateral growth, as the deposits become heavier. If thesurface being plated has an impression or depression therein, thereresults in the columnar, crystal structure a weakness perpendicular tothe impression where the columnar crystals come together. Most commonlyused addition agents retard the lateral growth of crystals, but due tothe retained columnar structure, the weaknesses in irregular surfacesremain. Thus, many addition agents.

result in a brittle electroformed structure which splits under thestresses to which matrices are subjected.

It is apparent that a desirable structure for electroformed deposits isone in which the columnar growth is retarded completely. I have foundthat if triethanolamine is added to a standard acid copper platingsolution, the resulting solution will produce fine-grain deposits bothlaterally and perpendicularly to the surface which is plated, thecolumnar crystal growth being retarded. Tensile tests made withspecimens of such copper deposits show a tensile strength equal to astrong copper alloy.

In accordance with my present invention, there is added to a more orless standard, acid copper plating solution triethanolamine in theproportions of approximately 0.7 ounce to 1 ounce per gallon of platingsolution. The plating solution may consist of approximately 25 ounces to32 ounces of copper sulfate and approximately 3 ounces to 10 ounces ofsulfuric acid per gallon of plating solution. The copper may be platedout in known manner at suitable current densities and suitable platingsolution temperatures. I have found that a copper deposit plated outfrom a solution according to my present invention has an extremely fineand uniform grain structure which gives the copper considerablestrength.

Copper deposits resulting from my improved plating solution have atensile strength of from about 60,000 pounds per square inch to about73,000

pounds per square inch with an elongation of approximately 6 per cent to9 per cent. This is about per cent stronger than known samples ofelectroformed copper obtained from standard, conventional, platingsolutions employing various addition agents proposed heretofore.

It will be apparent to those skilled in the art that the variousproportions of the addition agent indicated above. are not necessarilylimiting and that they may be varied more or less depending upon theparticular application or the particular articles to be plated. It willalso be obvious, no doubt, that my improved plating solution may beemployed in providing electroformed copper deposits on a great manyarticles other than phonograph record matrices, printing plates, and thelike.

I claim as my invention:

1. An acid copper plating solution consisting essentially ofapproximately 25 ounces to 32 ounces of copper sulfate, approximately 3ounces to 10 ounces of sulfuric acid, and an addition agent comprisingapproximately 0.7 ounce to 1 ounce of triethanolamine per gallon ofplating solution.

2. The method of producing on an article a fine-grain deposit of coppercomprising immersing said article in a solution consisting essentiallyof approximately 25 to 32 ounces of copper sulfate, approximately 3 to10 ounces of sulfuric acid and approximately 0.7 to 1 ounce oftriethanola (References on following page) I I I The followingreferences are of record in the Number. count Date file this 503,095Great Britain Mar. 31, 1939 UNITED STATES PATENTS OTHER'REFERENCESNumber Name Date I f 694,658 Meurant Mar. 4, 1902 f gf g 'ggfi gfl fi w1,642,238 Gardner Sept. 13, 1927 1,805,920 Muschler May 19, 1931 v2,391,289 Beaver Dec. 18', 1945

